1. Field of the Invention
The present invention relates to devices used to detect radiation. Specifically, the invention concerns apparatus and circuits that are used to detect and measure the radiation released from a radiological device, a so called dirty bomb, or associated with radioactive fallout following a nuclear or thermonuclear detonation.
2. Description of the Prior Art
Terrorist threats to the safety and stability of civilized countries have become an unfortunate reality of the modern era. The devastating attack upon the world trade towers in New York City clearly demonstrated that the nature of terrorist attacks has shifted in recent years. Formerly, modestly organized insurgent groups limited their attacks to small-scale targets, typically motivated by political interest, religious extremism, or the desire to release their captured cohorts. Today's terrorists are highly organized, well financed, multi-national organizations bent on the broad destruction of capital assets and the senseless mass killing of innocent noncombatants.
Modern terrorists have enbarked on a campaign to obtain and use weapons of mass destruction, or WMDs. One such WMD is the radiological device or ‘dirty bomb’. A dirty bomb consists of radiological material, such as low-grade uranium, and a disbursement means for distributing the radiological material over a large area, thereby indiscriminately exposing a population and inducing radiation sickness. In a typical dirty bomb, minimally processed uranium is packed around a core of conventional high explosive. Once the high explosive is detonated, a cloud of finely particulate radiological material is distributed over a moderately large area. Alternatively, the disbursement means may be a low-flying aircraft distributing fine particulates of radiological material.
A second WMD of concern is the nuclear or thermonuclear bomb. During a nuclear bomb detonation, nuclear fission is induced in highly processed uranium and/or plutonium. During a thermonuclear bomb detonation, nuclear fission is itself employed as a primer for the thermonuclear fusion of hydrogen isotopes such as deuterium or tritium. During both nuclear and thermonuclear detonations, enormous amounts of energy are released in the form of a destructive shock wave and fireball. Radiological material is ejected over a broad area as nuclear fallout causing radiation sickness long after the initial destruction. However, while nuclear and thermonuclear devices combine radiation poisoning with immediate, large-scale capital destruction, they are extremely complex devices requiring highly processed material, such as plutonium-238, and considerable technical expertise to construct.
Of the two WMDs identified above, the dirty bomb is considered the greatest potential threat due to the relative ease with which low-grade radiological material can be obtained and the low-technology associated with its disbursement means. Dirty bombs have the desired effect of creating terror to the public at large as well as incurring tremendous cost and clean up effort to make an affected area safe again as defined by government agencies such as the United States Environmental Protection Agency.
Accurate means for both detecting and quantifying the presence of radiological material are not known in general practice. Prior art detectors are analog devices based on Geiger counter techniques. Such Geiger counters are notoriously imprecise due to thermal drift instability in the circuit design. What is needed is a more precise, digital counter capable of accurately defining the normal background level at the installation and an elevated level due to the introduction of radioactive material. For a digital counter to work properly, a novel stable power supply is required since any drift in voltage may cause false alarms.